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Accueil du site → Doctorat → Allemagne → Towards an integrated crop management strategy for the African stalk borer, Busseola fusca (Fuller) (Lepidoptera : Noctuidae) in maize systems in Cameroon

Universitaet Hannover (1999)

Towards an integrated crop management strategy for the African stalk borer, Busseola fusca (Fuller) (Lepidoptera : Noctuidae) in maize systems in Cameroon

Ndemah, Rose Ngeh

Titre : Towards an integrated crop management strategy for the African stalk borer, Busseola fusca (Fuller) (Lepidoptera : Noctuidae) in maize systems in Cameroon

Auteur : Ndemah, Rose Ngeh

Université de soutenance : Universitaet Hannover

Grade : Doktors der Gartenbauwissenschaften Dr. rer. hort. 1999

Résumé
This study attempts to produce baseline data on importance and geographic distribution of stem borers and identify key interactions among and between abiotic (soil nutrients) and biotic (different life stages of pests, beneficials, host plants, vegetation indices, intercrops) factors in the stemborer ecosystem in Cameroon, which is a prerequisite for the development of evironmentally sound IPM-technologies. From 1993 to 1997, 297 farmers’ maize fields in six benchmarks in the forest zone and three benchmarks in the mid-altitude were visited periodically. In the forest zone only, the benchmarks were grouped into three blocks representing gradients in human population density and, thus, in length of fallow period. Five borer species were found on maize (Busseola fusca, Eldana saccharina, Sesamia calamistis, Mussidia nigrivenella and Cryptophlebia leucotreta) and four (B. fusca, E. saccharina, S. calamistis, Poeonoma serrata) on elephant grass, the most common wild host. Larvae and pupae per m2 of B. fusca were three to nine times higher on P. purpureum than on maize, whereas for E. saccharina the situation was the reverse. It was concluded that P. purpureum is not a good trap plant because larval mortalities were too low. Enumerative sampling procedures, based on Taylor’s power law, were developed for the most common pest species in order to make estimation of pest densities as cost-efficient as possible without losing accuracy. For any of the variables measured, there were no significant block effects in the forest zone ; within field variability was highest and between field variation contributed more to total variability than location, emphasizing the insular character of forest fields. In the forest zone, B. fusca was the predominant species during the first and E. saccharina during the second season. In the mid-altitude, B. fusca was predominant during both seasons whereas E. saccharina was not found in any of the fields. In both zones, negative relations could be found between cob weight and stem or ear damage, with B. fusca the most damaging species. B. fusca numbers at harvest increased with egg infestation but was negatively related to egg parasitism or parasitoid sex ratio earlier in the season. Soil Mg had a negative effect on yield by increasing B. fusca densities whereas egg parasitism had a significant positive effect. Increasing density of cassava in the system had a negative effect on B. fusca densities, probably because of increased mortality of migrating first instar larvae. Fifteen hymenopterous, two dipterous parasitoids and one fungal species were found. The scelionid egg parasitoids Telenomus busseolae and T. isis were the most common parasitoids and found in all locations in the forest zone. Most larval and pupal parasitoids belonged to the ingress-and-sting or planidial ingress guild. Cotesia sesamiae, the most common larval parasitoid of noctuid stem borers in eastern Africa was very scarce. Recommendations are given for further research into habitat management (management of soil nutrients, trap plants and intercropping with non-hosts), biological control options (‘redistribution’ approach, microbial control using viruses) and on how to increase uniformity of field infestations for host plant resistance screening.

Mots clés : Kamerun ; Tropischer Regenwald ; Maiszünsler ; Räumliche Verteilung ; Integrierte Schädlingsbekämpfung

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